1. Field of the Invention
The instant invention relates to a filter system for removing small amplitude, high frequency signals such as muscle artifact signals from an ECG signal, and more particularly relates to a filter system having a low pass filter with variable cutoff frequencies which cutoff frequencies are implemented in response to the detection of a QRS complex in an ECG signal.
2. Background of the Invention
A common problem in electrocardiography is the contamination of the ECG signal with artifacts from skeletal muscle tremors, which appear on the ECG signal as rapid, wavy deflections. These deflections render the electrocardiogram difficult to read. A common solution for the muscle artifact problem has been to pass the ECG signal through a low pass filter having a low cut-off frequency, typically approximately 25 Hz. Since muscle artifact signals typically have significant energy at frequencies higher than 25 Hz, the low pass filter effectively reduces the muscle artifact signal. However, the low pass filter has the disadvantage of reducing the amplitude of the QRS complex because the high frequency components of the ECG signal necessary to describe the relatively high peaks of the QRS signal are also removed as the ECG signal passes through the low pass filter.